1. Field of the Invention
The invention relates to inks that can be used for the marking and decoration of objects that have to be brought to high temperatures, such as objects made of ceramic type material. The inks according to the invention are particularly capable of being used for the marking or decoration of objects by ink jet.
Ink jet printing is a well known technique that enables the high-speed marking and decoration of all kinds of objects, without contact between the printing device and these objects. The printing devices may be of the "Drops on Demand" (D.O.D.) type or of the "continuous ink jet" type.
2. Description of the Prior Art
The ingredients of presently used inks are organic products, dyes, pigments or resins that are dispersed in solvents of varying volatility or in water. None of these ingredients, except for titanium oxide used in white inks, can withstand temperatures of over 300.degree. C. for more than a few minutes.
Now, the ceramics manufacturing industry uses techniques for the sintering or melting of powders in which the objects are brought to temperatures of at least 500.degree. C., and possibly of up to 1300.degree. C. and more: this means that inks containing organic products cannot be used.
Before the above-mentioned heating operation, the objects are generally pulverulent and cannot be handled without the risk of being damaged on the surface. Hence, when these objects have to be referenced, marked or decorated indelibly, the manufacturers make use of either modifications of the relief of the objects before baking or a first baking operation at low temperature so that they can be handled and are not pulverulent on the surface.
Then, markings or decorations are applied to these partially fired objects, notably by decal or transfer process. The colors of these decal operations are given by exclusively mineral pigments which are resistant to the baking temperatures of these objects. Mineral pigments of this kind are combinations of metallic oxides which, by their particular crystal structure, like that of spinels, have different and varying colors.
A non-exhaustive list of the most commonly used metals, with colored or opaque oxides, would include iron, chromium, copper, cobalt, manganese, antimony, titanium, zirconium, tin and vanadium, these metals being used alone or combined with each other or, again, combined with metals like silicon, magnesium, the oxides of which are not colored.
For the decoration of ceramics, it has been proposed to use the ink jet printing method (cf. article by W. Roberts in the journal "L'INDUSTRIE CERAMIQUE" No. 827.5/88) by using the same pigments as those used in the standard printing of ceramics as indicated here above. In a method such as this, the main problem to be resolved is the one related to the great difference in density between the pigment and the liquid in which it is dispersed.